All dogs are great, each breed or mix has their own plusses and minuses, and almost every dog can be a great match for the right person.

That said, the answer that popped out as soon as I read this thread's title was:

Sheba! The doggie I grew up with, she was maybe a Shepherd/Doberman mix, maybe Shepherd/Rottie. A slightly bulkier German Shepherd. In any case, she was the best, smartest dog in the whole wide world. She taught me so much, like looking both ways before I crossed the street, like it's okay if the older kids won't play with you, you still have Sheba dog, and I have never met a better dog. She made a dog-lover out of the man across the street who "didn't like dogs," she protected us if we kids were outside but parents were inside, she kept the neighborhood free of woodchucks (and anything else she could catch, she had a high prey drive) and um, even improved the genetics of the neighborhood cats - the smart ones, the fast ones - those were the ones who lived to reproduce. (Sorry cat folks, no offense intended.) Sheba was the best (non)breed of dog ever.